Kinetic investigations of the effect of catalytically active minerals in biomass-derived solid fuels on pyrolysis and char conversion under oxy-fuel conditions

It is well known that K, Na, Fe, Mg, and Ca affect biomass oxidation and gasification including the Boudouard equilibrium. The enlargement of the volume flow due to the enhanced reaction rate by the catalytically active minerals influences the flow field of flames and has to be taken into account.

The project A5 investigates the catalytic effects of minerals present in biomass-derived solid fuels on the kinetics of pyrolysis and char burnout in Oxy-Fuel atmospheres. The catalytic effects are analyzed as a function of the mineral matter type and its loading including synergetic and opposing interactions of multiple components and taking the influence of different counterions into account. The chemical transformations of the catalytically active inorganic species during pyrolysis and char burnout are monitored in detail to account for their influence on the catalytic properties.

Within FP1, the catalytic effect of single minerals in O2 was successfully investigated using a model fuel with lignite-like oxidation behavior, which was derived from cellulose. As this is a main component of biomass, it was possible to use the well-characterized model fuel also in biomass-related investigations within FP2. To represent Oxy-Fuel conditions, investigations in O2 were supplemented by gasification experiments in H2O and CO2 mainly using a thermobalance. Therefore, it was possible to assess the catalytic effects of alkali, earth alkaline, and iron ions depending on the gas-phase composition.

In FP3, the established systematic approach will be extended to well-defined mixtures of biomass-relevant components obtained by hydrothermal carbonization and fast pyrolysis as well as of typical minerals in order to derive a quantitative description of the kinetic effects and their correlation with physico-chemical properties. This approach includes pyrolysis product distributions obtained in a heated strip reactor and a multidimensional pyrolysis-GC/MS system as well as changes in the burnout kinetics, which will be used to extend the CPD, the CCK, and the CRECK-S-B model in the CRC by catalytic effects.